Difference Between Dehydration Synthesis and Hydrolysis

Main Difference – Dehydration Synthesis vs Hydrolysis

Chemical reactions can be categorized into different groups according to the properties of those reactions. Dehydration synthesis and hydrolysis are such chemical reactions. These reactions are categorized according to their mechanism. Both these reactions involve either synthesis or consumption of water molecules. The main difference between dehydration synthesis and hydrolysis is that dehydration synthesis results in the formation of a large molecule out of smaller molecules whereas hydrolysis results in the formation of smaller molecules out of a large molecule.

Key Areas Covered

1. What is Dehydration Synthesis
      – Definition, Mechanism, Examples
2. What is Hydrolysis
      – Definition, Mechanism, Examples
3. What is the Difference Between Dehydration Synthesis and Hydrolysis
      – Comparison of Key Differences

Key Terms: Carboxylic Acid, Condensation, Dehydration Synthesis, Esterification, Glycosidic Bond, Hydrolysis, Peptide Bond

What is Dehydration Synthesis

Dehydration synthesis is the formation of a larger molecule with the release of water molecules. Here, two or more smaller molecules form covalent bonds with each other, releasing a water molecule per each bond. Therefore, the final products of dehydration synthesis reactions are always complex compounds than that of the reactants. Dehydration synthesis reaction is a type of synthesis reaction since a large molecule is produced.

These dehydration synthesis reactions can also be named as condensation reactions since condensation refers to the formation of water molecules. Therefore, dehydration synthesis occurs between molecules having a hydroxyl (–OH) group and a proton that are available to be released.

In chemical synthesis processes, dehydration synthesis is used to obtain larger molecules through releasing water molecules. For example, the reaction between an alcohol and a carboxylic acid may produce an ester, releasing a water molecule as the byproduct. Here, the –OH group of the carboxylic acid is released and the –H atom bonded to the oxygen of alcohol is also released. Therefore, these two –OH group and –H group combine to form a water molecule.

Figure 01: Esterification

In biological systems, the terms glycosidic bonds and peptide bonds are often used to describe the bonding between molecules. Glycosidic bonds are formed as a result of the reaction between two monosaccharides releasing a water molecule whereas peptide bonds are formed as a result of the reaction between two amino acids releasing a water molecule. Therefore, these are condensation or dehydration synthesis reactions.

What is Hydrolysis

Hydrolysis is cleavage of a chemical bond in the presence of water. Here, water act as a reactant that is involved in the reaction process. In hydrolysis reactions, a large molecule is always broken down into smaller molecules. Therefore, the reactants always include a complex molecule, unlike products. In these reactions, a water molecule is added to the reactant molecule, which causes the cleavage of a chemical bond present in that reactant.

When a large molecule is hydrolyzed, the resulting two small molecules get a –OH group and a –H group from the water molecule. Hydrolysis is the opposite of condensation. This is because, in condensation reactions, a water molecule is formed whereas in hydrolysis a water molecule is consumed.

Figure 2: Ester Hydrolysis Reaction

If we take the same example as in dehydration synthesis reaction, hydrolysis of an ester forms the reactants of esterification reaction. They are the carboxylic acid and alcohol. For this, a base is used. Therefore, carboxylate ion is formed instead of carboxylic acid due to its high stability. However, this reaction consumes water molecules in order to provide –OH group for the carboxylic acid formation and the –H group for the alcohol formation. This process is called saponification.

Difference Between Dehydration Synthesis and Hydrolysis

Definition

Dehydration: Dehydration synthesis is the formation of a larger molecule with the release of water molecules.

Hydrolysis: Hydrolysis is cleavage of a chemical bond in the presence of water.

Mechanism

Dehydration: Dehydration synthesis reactions are combination reactions.

Hydrolysis: Hydrolysis reactions are decomposition reactions.

Water Molecule

Dehydration: Dehydration synthesis reaction forms a water molecule.

Hydrolysis: Hydrolysis reaction consumes a water molecule.

Reactants

Dehydration: The reactants of dehydration synthesis reactions are smaller molecules than their products.

Hydrolysis: The reactants of hydrolysis reactions are complex molecules than their products.

Byproducts

Dehydration: Dehydration synthesis reactions give water molecules as byproducts.

Hydrolysis: Hydrolysis reactions do not give byproducts.

Conclusion

Both dehydration synthesis and hydrolysis are chemical reactions that are occurred in the presence of water. That is because dehydration synthesis reactions provide water molecules to the medium whereas hydrolysis reactions consume water molecules from the reaction mixture. The main difference between dehydration synthesis and hydrolysis is that dehydration synthesis results in the formation of a large molecule out of smaller molecules whereas hydrolysis results in smaller molecules out of a large molecule.

References:

1. Reid, Danielle. “Dehydration Synthesis: Definition, Reaction & Examples.” Study.com. n.d. Web. Available here. 09 Aug. 2017. 
2. “Hydrolysis.” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 09 Aug. 2017. 

Image Courtesy:

1. “Esterification” By Toby Phillips – Own work (Public Domain) via Commons Wikimedia
2. “Ester hydrolysis” By SVG version: WhiteTimberwolfPNG version: Bryan Derksen, H Padleckas – Ester hydrolysis.png (Public Domain) via Commons Wikimedia